Some ignition coils for internal combustion engines include a coil section that is disposed outside a plug hole. The coil section includes a primary coil and a secondary coil. The secondary coil includes a high-voltage winding end portion that is connected to an ignition coil disposed within the plug hole using a pole joint or the like.
For example, PTL 1 discloses a structure of an ignition coil device for an internal combustion engine in which a high-voltage tower of an ignition coil and a spark plug in a plug hole are connected to each other by a high-voltage joint. A protrusion is formed to protrude in an outer periphery of the high-voltage joint. The protrusion is pressure-welded to the inner peripheral surface of the plug hole so that the high-voltage joint is located at a center of the plug hole.